1. Field
The present invention relates to disk drives for computer systems. In particular, the present invention relates to a disk drive seeking to an outer diameter (OD) track and then ramping velocity to implement fast unload.
2. Description of the Related Art
A disk drive comprises a disk rotated by a spindle motor and a head (or heads) actuated over the disk by a voice coil motor (VCM) in order to write/read data to/from the disk surface. When the spindle motor spins down the disk, for example, just prior to the disk drive being powered down or entering an idle mode, the heads may be unloaded off the disk onto a ramp that extends over an outer diameter of the disk. When the disk drive is powered on or exits the idle mode, the spindle motor spins up the disk and the heads are loaded off the ramp onto the disk.
Free fall detection has also been implemented in disk drives employed in mobile devices, such as laptop computers. When a free fall is detected (e.g., when the mobile device is dropped), the disk drive executes an unload operation in order to unload the heads as quickly as possible to avoid damaging the heads upon impact. To ensure that virtually all real free fall conditions are detected, the sensitivity of the circuitry and algorithm for detecting the free fall condition is typically set very high, which means the free fall condition may be detected many times per hour even though the mobile device may not be dropped or otherwise in danger of being damaged. This can significantly increase the number of unload operations executed by the disk drive which can reduce its lifetime due to ramp wear, suspension wear, head vibrations, and gimbal separation from the suspension.
There is, therefore, a need for a disk drive employing a fast unload operation for free fall detection while minimizing undesirable component degradation.